Process for the manufacture of water-hardening material reinforced with open meshed films

ABSTRACT

An improved process for the manufacture of reinforced shaped articles from water-hardening materials. A plurality of continuous networks of synthetic organic polymer material having at least two meshes per square centimeter are incorporated in said water-hardening materials as reinforcement. The networks are prepared by forming meshes in an unfibrillated film of the synthetic organic polymer material.

This is a division of application Ser. No. 26,221 filed Apr. 2, 1979.

BACKGROUND OF THE INVENTION

The invention relates to an improved process for the manufacture ofsheets and other shaped articles from a water-hardening material, suchas cement and gypsum, reinforced with continuous networks of syntheticorganic polymers incorporated therein.

The term "water-hardening material" as used herein refers to a mixtureof a dry or substantially dry binder and water, optionally containingaggregates, that can be hardened or bound into a solid rigid mass byreaction between the binder and water. The term also applies to thehardened material after setting. Suitable binders include, for example,various types of cement, gypsum and other similar material such asPortland cement, aluminum cement, plaster of Paris and anhydrite.

It has been proposed in Netherlands patent application No. 7,707,253 toprepare sheets and other articles from reinforced water-hardeningmasses, wherein the reinforcement consists of networks of continuousfibrillated organic film. It has been found that the incorporation ofsuch networks results in a surprisingly significant improvement in thestrength of the water-hardening material. However, it appears that thestrength is not equally high in all directions. Although high strengthscan be achieved in the direction of fibrillation, the strength isconsiderably lower normal to this direction. This is possibly due to theinstability of the knots or intersections of the filaments forming thenetwork. This disadvantage can be overcome by the use of combinations ofnetworks arranged normal to one another, but this renders the process offabricating the final articles considerably more complicated.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a process that yieldsproducts of excellent strength in all directions. A further object is toprovide a process for making articles from water-hardening materialshaving excellent strength properties at a comparatively low cost. It hasnow surprisingly been found that these and other objects can be achievedby the incorporation of continuous unfibrillated networks inwater-hardening materials, which networks are formed from syntheticorganic polymer films having at least two meshes per cm², preferably atleast 3, and most preferably at least 10 meshes per cm².

As used herein, the term "continuous unfibrillated networks" refers tonetworks that are not fibrillated, that is, the meshes are not separatedonly by fibrils. Rather, the networks are formed by other means such asby removing portions of the plastic film or by pushing portions of theplastic film aside. This results in the network having a greaterstability, particularly at the intersection or knots of the filmportions forming the network. Such networks, as used in the invention,extend across a large dimension of the article in which the network isincorporated, that is, its length or width.

If the meshes are completely shaped and surrounded by fibrils thestrength of the resulting network is not uniform. However it has beenfound that the continuous unfibrillated networks of this invention giveat least the strength of networks formed from fully fibrillated films,and additionally offer the advantage of more uniform strength in alldirections, and hence a higher and more uniform strength of the productsin which they are incorporated. Furthermore, the number of meshes insuch networks can be more accurately controlled, as well as the shapeand size of these meshes. This is very important inasmuch as it has beenfound that the number of meshes has a decisive effect on the finalstrength properties of the manufactured articles. Furthermore, thegreater mechanical strength of the continuous unfibrillated networks ofthis invention facilitate their handling during the manufacture ofarticles of reinforced water-hardening material in which they areincorporated.

DETAILED DESCRIPTION OF THE INVENTION

The networks used in this invention are made by first processing thesynthetic organic polymer into a film by conventional means, such as byan extruder or by use of calenders. The sheets of film are preferablyvery thin, ranging in thickness from about 2 to 250 μm, particularlyfrom about 5 to 100 μm.

The plastic material used to form the films from which the continuousunfibrillated networks are formed may be a polyolefin, such aspolyethylene and polypropylene, as these polymers possess some veryfavorable properties rendering them particularly suitable for use asreinforcement in water-hardening materials. If polypropylene is used, amaterial is preferably chosen having a melt index in the range ofbetween 1 and 15, most preferably between 2 and 9 dg/min. Whenpolyethylene is used, the melt index preferably ranges between 0.01 and10, particularly between 0.02 and 0.2 dg/min.

Also thermoplastic materials that form films and fibers, such aspolymers of styrene or vinyl chloride, or copolymers thereof may beused. Partly crystalline polymers may be used as well. Specialpreference is given to modified or unmodified polyolefins. Examples ofsuitable modified polyolefins are chlorinated polyethylene andpolypropylene. Polypropylene homopolymer has been found to be mostsuitable, although copolymers and block copolymers, for example withethylene, may also be used, as well as mixtures of polymers.

The polymer utilized may also contain various types of fillers andauxillary substances such as carbon black, polar substances, pigments,light and heat stabilizers and antioxidants. It has been found veryimportant that the correct stabilizers are incorporated in the networks,and favorable results have been achieved with a combination of a metaldeactivator and an antioxidant. These compounds are used in amounts offrom 0.001 to 2.5% by weight, preferably from 0.01 to 1% by weight. Thepreferred metal de-activators are complexing agents, some examples ofwhich are phosphoric acid, citric acid, ethylene diamine tetra-aceticacid or a salt thereof, N,N'-disalicylidene ethylene diamine, lecithin,gluconic acid, hydrazine derivatives and oxanilide derivatives,particularly N,N'-bis (3,5-ditert-butyl-4-hydroxyphenyl) propionylhydrazine. Preferably citric acid, whether or not free of water, ischosen as the metal de-activator.

The antioxydants are preferably non-phenolic ones, for instance amines,particularly aromatic and secondary amines, such as N,N'-disubstitutedp-phenylen diamines, diphenyl amine derivatives, amino-phenolderivatives, condensation products of aldehydes and amines or of ketonesand amines. Further suitable antioxidant compounds include sulfurcompounds such as mercaptans, thioethers, disulphides, anddithiocarbamates, zinc dimethyl dithiocarbamate being an example. Alsophosphorus compounds, such as derivative of phosphoric acid ordithiophosphoric acid, may be used. However, preference is given to thegroup of amines.

This invention also contemplates the use of film materials which mayhave been treated with, for example, radiation such as UV light andcorona discharge, or oxidizing acids such as chromic acid, to obtainadhesion between the network and the water-hardened mass.

Before the meshes are made in the film, it is advantageous to stretchthe film uniaxially or biaxially. This offers various advantagesincluding a considerable increase in strength and at the same time areduction in the thickness of the film. The meshes may be made in thefilm in a number of ways. It has been found, however, that optimumresults are obtained when the plastic material is pushed aside, being ina plasticized state, and/or removed mechanically. Methods in which thefilm is notched or perforated, without removing material, have beenfound to give less favorable results. These latter methods producemeshes having very sharp corners such that the stability and strength ofthe knots or intersections are less than desired. The corners of themeshes according to the present invention are preferably over 45°,especially over 60°, and most preferably about 90°. Meshes withoutcorners have also strong preference.

The networks used in this invention are preferably made by processing asynthetic organic thermoplastic polymer into a film, plasticizing thisfilm by heating it at least in the places where the meshes will beformed, and then pressing the material away, followed by stretching thefilm after mesh formation. It is also advantageous to stretch the film,such as lengthwise, before the meshes are made. Preferably the plasticmaterial is pressed away along the length of the film so that athickened edge or ridge is formed, after which the film is stretched ina direction normal to its length. This has the effect of eliminating thethickened edges or ridges. The pushing aside of the plasticized materialcan be advantageously accomplished by means of two or more rollers, atleast one of which is smooth. Another roller pressing against the firstis provided with protrusions or teeth. This latter roller, also called apunch roller, preferably has a peripheral speed that is 25 to 50% lowerthan that of the mating smooth roller. It is also possible to use hotrollers that serve to plasticize the film, however the punch roller ispreferably cooled.

If the film must be heated in order to plasticize it, its mechanicalstrength becomes very low so that problems may arise in handling thefilm. It is therefore preferable to reinforce the film in one way oranother if high production speeds are to be achieved. A particularlyattractive way of reinforcing the film is to apply filaments of amaterial that does not melt, or melts at temperatures higher than thepolymeric material out of which the film is made. These filaments mustbe incorporated lengthwise in the film. The meshes can then be made inthe film in between the continuous filaments of the material having thehigher melting point by pushing the plastic material aside into athickened edge or ridge. It is advantageous that the reinforced film haspreviously been stretched lengthwise.

After the meshes have been made, the film can again be stretchedlengthwise. It is also desirable to stretch the film broadwise, in adirection normal to its length in order to eliminate the thickened edgesor ridges. It is furthermore possible that the film would then be in astate of imminent of fibrillation. In this embodiment, good and stablenetworks may be obtained when the total degree of stretching is about 3to 10 times lengthwise, and about 5 to 15 times crosswise or normal tothe length.

It has been found that very suitable combinations of film material andhigher melting filament material include polyethylene as the filmmaterial in which polypropylene, polyamide and/or polyester filamentshave been applied, as well as polypropylene film in which polyamideand/or polyester filaments have been incorporated. Care must be taken,however, when polymers such as polyamides and/or polyesters areincorporated in the strongly alkaline water-hardening materials,inasmuch as these polymers are very susceptible to hydrolysis in such amedium. This can be done, however, only if these polyamides and/orpolyester filaments are fully embedded in or fully surrounded bypolyolefins.

After the meshes have been formed in the film, the film can be stretcheduniaxially or biaxially. By stretching after the meshes have been found,the meshes can be enlarged and accumulated material, if any, can besmoothed out. Other advantages of biaxial stretching include theenlargement of the originally small meshes to a size of at least 100 μm,preferably at least 300 μm in diameter, which results in a furtherimprovement in the strength properties of the article formed.

It is of particular importance that the films have a sufficiently largenumber of meshes to achieve the desired strength of the ultimate articlein which they are incorporated. Thus the film network will have at leasttwo meshes per cm², preferably at least three, and most preferably atleast 10 meshes per cm². The number of meshes per unit volume of thefinished product is also of particular importance. If this number issufficiently high, excellent mechanical properties are achieved,particularly excellent resilience and retention of physical properties.Thus the number of meshes in films of organic synthetic polymerincorporated in the final product is preferably at least 100 per cm³ ofthe final product. Preferably this number will exceed 200, and mostpreferably will be at least 300 meshes per cm³. In fact best results areobtained if this mesh density or concentration is over 500 meshes percm³ of the finished product.

It is also advantageous to use networks having a large specific surfacearea in addition to a large number of meshes. This can be achieved byutilizing networks that are not smooth, and that have many protrudingloose fibrils, so that the network has a coarse or hairy texture. Thespecific surface area of the network is preferably at least 1 mm² /mm²and preferably at least 3 mm² /mm². The specific surface area of thenetworks per unit volume of the end product should be at least 10 mm²/mm³, and most preferably at least 25 mm² /mm³. This large specificsurface area also contributes to improvement of the multiple crackingcharacteristics during pseudo-plastic deformation of the article, or inother words, an increase in the number of microcracks and a decrease intheir size upon deformation. This phenomenon has a very favorable affecton the properties of the end product, particularly contributing to itssuperior ability to readily regain its former shape after deformation.

The water-hardening material in which the networks are incorporatedcontains a water-hardening binder, aggregates if desired, and water. Therelative amounts may vary within wide limits, but the ratio between theamount of water and the amount of water-hardening binder generallyranges between about 0.2 and 10. The aggregates used, particularly sand,should preferably be so fine that the average particle size is less than1 mm, and the amount used may be varied within wide limits. The ratiobetween the amount of water-hardening binder and the amount ofaggregates preferably ranges between about 0.05 and 3.

Various aggregates and/or auxillary substances may be added towater-hardening material including sand, gravel, chalk, powdered quartz,plastic waste, sulfur, clay, fibers, vulcanized or unvulcanized rubber,rock wool, glass wool, hardening accelerators, pigments and processingaids. It can also be PG,11 advantageous to add polyvinyl alcohol orpolyvinyl acetate to the suspension of water and binder, which may havea favorable effect on the oxygen impermeability of the finished article.These latter additives furthermore serve to better protect the plasticof the network against oxygen diffusing into the article which isparticularly important when polypropylene networks are used.

The water-hardening material may additionally contain auxiliarysubstances to improve or accelerate its processing into the endproducts. Such auxiliary substances include so-called deflocculants orother surfaces-active agents, hardening accelerators or retarders, andthickeners. These auxiliary substances may also be incorporated in thefilm material from which they can be slowly released in a controlledmanner. Furthermore, other additives such as flame-retarding and/orflame-proofing agents may be incorporated in the water-hardeningmaterial and/or the plastic film from which the network is made. Forexample, antimony trioxide and chlorinated and/or bromonated compounds,either together or separately, may be processed into one or both of thecomponents.

The process of this invention can be effected either continuously ordiscontinuously. It should be apparent, however, that they cannot bemade in the conventional manner used in the manufacture ofasbestos-cement products, wherein a suspension of water-hardeningmaterial and fibers are mixed to a homogeneous consistency in normalrotating mixing equipment and thereafter processed into layers andhardened. The continuous unfibrillated networks of the present inventionof course prevent the utilization of such equipment. Therefore othertechniques must be used to build the articles of this invention.

The discontinuous method involves placing alternate layers ofwater-hardening material and the continuous unfibrillated networks ontop of one another until a satisfactory layer thickness has beenobtained. However such a hand-building method is time consuming andcostly.

Alternatively, the articles may be made in a continuous way bycontinuously unwinding a network contacting it with a water-hardeningmaterial and rolling it, together with the water-hardening material,onto a forming roller until the desired layer thickness has beenreached. The layered material thus formed can then be put into thedesired shape and hardened. It is also possible to manufacture hollowarticles by winding one or more networks around a mandrel while thewater-hardening material are continuously applied to the networks eitherby emersion or spraying.

A particularly preferable continuous method for forming the articleswithin the scope of this invention involves (a) forming continuouslengths of networks from unfibrillated organic films, each of whichcontains a plurality of meshes; (b) simultaneously advancing a pluralityof such networks into contact with the water-hardening material so as toform a composite layer of such networks and the water-hardeningmaterial; and (c) shaping this composite layer into the desiredconfiguration and allowing it to set. This method permits the formationof an article containing multiple layers in one operation without theneed for a time consuming and expensive hand-building method.

Continuous lengths of unfibrillated networks may be supplied to such aprocess from a reel onto which they have been wound. Alternatively, thenetworks may be formed directly from the outflow from an extruder headin film form, in which film meshes are formed to prepare the networks,and thereafter contacting such networks with the water-hardeningmaterial to form the articles.

The contacting of networks with the water-hardening material can beaccomplished by various methods. These include pouring in which asuspension of the water-hardening material is formed and poured, bymeans of a distributor, onto the networks as they are unwound andadvanced through the process. Alternatively, the various components ofthe water-hardening material may be applied by spraying or sprinkling.Any excess water present can be removed for example by vacuum through aporous material, and the resulting layer of networks and water-hardeningmaterial is then compacted by vibration and/or compressing so thatbetter coherence is obtained. The layer is thereupon shaped into thedesired configuration for the ultimate shaped article and permitted toset. Alternatively, a number of such layers can be formed, continuouslybrought together, compacted, shaped, and allowed to set, in order toform a shaped article of greater thickness.

As used herein, the term "continuous" should be understood to includenot only the use of such continuous networks formed by the directoutflow from an extruder, but also discrete lengths of such films whichcan be fed into the process from, for example, a reel, but whichnetworks have a length many times longer than the length of the ultimatearticle. Consequentially, the networks used in the invention consist ofcontinuous networks which extend virtually over the entire majordimensions of the shaped article.

The articles made according to the present invention may contain notonly the reinforced water-hardening mass as above described, but alsoother materials such as foamed polymers or other foamed, expanded orlight materials can be incorporated into the product formed. Examples ofsuch materials are expanded polyethylene, polypropylene, polyvinylchloride, polystyrene or polyurethane, and mineral materials such asperlite, rock wool or glass wool. The additional layer or layers ofthese materials can impart insulating properties to the products, aswell as lower weight, lower price and better protection against moistureand impacts or blows. These additional layers or sheets can be suppliedeither continuously or intermittently or can be formed in situ, afterwhich the reinforced water-hardening layer is applied. Alternatively,such additional layer or sheet of foam may be applied to the formedlayer of water-hardening material and networks.

If desired, a light and/or foamed or expanded material may be processedas an aggregate added into a previously prepared suspension of thewater-hardening binder, water and any other aggregate or additives. Itis also possible to foam the suspension containing the water-hardeningbinder itself.

Another application of the products of the present invention is to usethem together with fillers incorporated as a separate layer in theultimate product. An example of such a composition would be anunreinforced inner layer of gypsum or other water-hardening materialsurrounded by layers of water-hardening material reinforced withnetworks. If desired, the inner layer itself may also be provided,perhaps to a lesser extend, with a network reinforcement. It is alsopossible to apply separate cement layers of different composition, forexample, one or more cement layers containing glass beads.

The density of networks in the final product, expressed as a % by volumeof the final product, ranges between about 0.25 and 20%, but moresuitably between about 2 and 15%. Preferably, however, the density ofnetworks in the final product will range between about 3 and 10%. Itshould be understood that different portions of the final product mayhave different densities. For example, very suitable articles can bemade by utilizing the above network concentration or density in theouter layers only. In such instance, the outer reinforced layer shouldhave a thickness of at least about 1 mm and contains at least fivenetworks.

EXAMPLE

Sheets were made of Portland cement reinforced with unfibrillatednetworks of polypropylene in which polyamide filaments were incorporatedlengthwise. The meshes are made by pushing aside plastic material andstretching the film. The network thus obtained had 16 more or lessrectangular meshes per cm² and had a specific surface area of 4 mm²/mm². Seven such networks were incorporated per mm of thickness of thefinished sheet, which resulted in 1120 meshes per cm³ of end product.The content by volume of the network was 7%, and the specific surfacearea was 25 mm² /mm³. The networks were soaked in a suspension ofPortland cement A, water and sand. The sand particles had a size ofbetween 100 and 200 μm. The water-cement factor (WCF) was 0.75 and theamount of sand was 20% by weight relative to the cement. The layer wasthen pressed and cut. The WCF of the cut sheet was 0.25.

The properties of the moulded sheet were measured after 28 days' settingat a relative humidity of 95% by means of a four-point bending test.Lengthwise the bending strength was 26 N/mm² and, normal to the length,it was 17 N/mm² resulting in a ratio of 1.5. Loading gave rise to veryfine multiple cracking, resulting in a very smooth bending curve.

COMPARATIVE EXAMPLE

A sheet made by using fibrillated networks according to European patentapplication No. 78200392.5 resulted in a ratio between lengthwisebending strength and bending strength normal to the length of 2.5.

What is claimed is:
 1. A shaped article comprised of at least one layerof a water-hardening material reinforced with at least fiveunfibrillated organic films which have been provided with meshes so asto form networks, each having a plurality of said meshes, wherein thenumber of networks in said layer and the average number of meshes insaid networks with a minimum of three per square centimeter are suchthat the average number of meshes per cubic centimeter of said layer isgreater than
 200. 2. A shaped article comprised of at least one layer ofa water-hardening material reinforced with at least five unfibrillatedorganic films, which have been provided with meshes that are formed in amanner so as to avoid sharp corners to form networks, each having aplurality of said meshes, wherein the number of networks in said layerand the average number of meshes in said networks with a minimum ofthree per square centimeter are such that the average number of meshesper cubic centimeter of said layer is greater than
 300. 3. A shapedarticle comprised of at least one layer of a water-hardening materialreinforced with at least five unfibrillated organic films which havebeen provided with meshes that are formed in manner so as to avoid sharpcorners to form networks, each having a plurality of said meshes,wherein the number of networks in said layer and the average number ofmeshes in said networks with a minimum of three per square centimeterare such that the average number of meshes per cubic centimeter of saidlayer is greater than 500.